Additional low-frequency modes in zirconium hydrides

Vibrational modes in ZrH0.1 were studied by neutron spectroscopy at room temperature (α-Zr and γ-hydride) and around 528 K, the FCO γ-phase to FCC δ-phase conversion temperature given by the literature. The optical mode analysis in terms of H vibrations specific to each hydride agrees with recent neutron-diffraction and specific-heat measurements, indicating a lower temperature for this phase transition. Using different experimental resolutions, the inelastic scattering was well-separated from the quasielastic one. Additional low-frequency modes (at around 5 meV), revealed by spectra measured at all temperatures, are discussed in terms of strong overdamped phonons confined to an interstitial H and its surrounding nearest neighbors and characteristic of resonant vibrations.